The HDMI (High Definition Multimedia Interface) has been known as a data interface standard for transmitting video and audio signals (digital contents) in digital form.
As is well known, the HDMI is a standard based on the DVI (Digital Video Interface) established as a standard for connecting a personal computer with digital display devices such as a liquid crystal display device digitally driven for display, the HDMI being worked out additionally to include features such as those for audio transmission, copyright protection, and color difference transmission in order to serve as a standard for digital video and audio input and output applicable primarily to household appliances and AV (Audio Visual) devices. According to the HDMI, a transmitting (output) device is referred to as a source and a receiving (input) device as a sink. Video and audio signal data are transmitted under the HDMI not bidirectionally but unidirectionally from the source to the sink. It should be noted however that when a control signal path called DDC (Display Data Channel) is used, bidirectional communication is available.
For example, a user may set up an AV (Audio Visual) system by connecting at least two HDMI-compatible devices by means of an HDMI cable or the like (Japanese Patent Laid-Open No. 2002-311933).
However, as mentioned above, the data transmission according to the HDMI can only be unidirectional from the source to the sink. This can be a constraint on the user's attempt to build a desired AV system. For example, the user may want to have data transmitted from a device A and received by a device B, but it might happen that the device A is equipped only with an input (receiving) terminal and has no output (transmitting) terminal, or that the device B is furnished only with an output terminal and has no input terminal.
Such an inconvenience may be eliminated conceivably by providing additional receiving and transmitting terminals to the HDMI devices. At present, however, the devices and cables compatible with the HDMI are more expensive than those of other data interfaces. Thus, adding HDMI terminals indiscriminately is not preferable in terms of cost.
An object of the present invention is illustratively to provide a more flexible system which primarily adopts the unidirectional data transmission such as that according to the HDMI while also permitting typically bidirectional transmissions without fail.